This invention relates to an over-running clutch, preferably for use in a manual shift type automotive transmission, which will prevent a vehicle from rolling down a hill when the vehicle starts from a stopped position on the hill. More specifically, the present invention relates to an over-running clutch assembly of a roller/ramp variety which can be controlled for selectively locking up the drop shaft of an automotive transmission.
Vehicles with manual transmission have a tendency to roll backwards before accelerating forwards after being stopped on an uphill grade. The driver of the vehicle must accelerate the vehicle smoothly by relieving brake pressure while engaging the clutch to avoid tolling backward into a vehicle positioned behind their own. Preferably, this is done without excessive clutch slippage and without stalling the vehicle. Often, however, the time to transition the right foot from the brake to the throttle pedal and to begin clutch engagement in sufficiently long enough to allow rearward motion to begin. Therefore, the clutch engagement must change the rearward motion of the vehicle to forward motion and then accelerate the vehicle up the hill. In attempting to of this quickly and smoothly without stalling the vehicle, a driver will often overcompensate with a combination of excessively high engine speed and excessive clutch slippage, thereby resulting in increased clutch wear and reduced clutch life.
Current attempts to alleviate this problem using a hydraulically actuated ratchet type device, mounted onto a shaft of an automotive transmission, to prevent rollback of the vehicle. Current devices of this type exhibit reliability issues related to the hydraulic valve and often fail prematurely. Additionally, devices of this type do not disengage immediately upon forward motion, thereby causing a noticeably ratcheting noise as the vehicle begins forward motion.
It would be desirable to provide a device mounted within an automotive transmission that would prevent rearward motion of a vehicle as the vehicle starts from a stopped position on an uphill grade.
A primary object of this invention is therefore to provide an over-running clutch mechanism, such as that disclosed in U.S. Pat. No. 5,927,456 or U.S. Pat. No. 5,924,510, installed within the manual transmission of an automotive vehicle which, when engages, will lock a shaft of the transmission to prevent the vehicle from rolling backward. The device can be selectively actuated by an electromagnetic trigger clutch of by hydraulic, pneumatic or other means.
In accordance with an aspect of the present invention a clutch assembly comprises an outer race fixedly mounted within a transmission having a cylindrical inner surface and being rotatable about an axis, an inner race engaging a shaft of the transmission and having a cammed outer surface coaxial with the cylindrical inner surface and defining a gap therebetween. The inner race is rotatable about the axis with rotational movement relative to the outer race. A plurality of cammed surfaces are formed at spaced apart locations on the outer surface of the inner race. A plurality of rolling elements are positioned between the outer race and the inner race with one of the rolling elements being located at a midpoint of each of the cam surfaces and each of the rolling elements having a diameter less than the gap between the midpoint of the cam surface on the inner race and the cylindrical inner surface of the outer race. A retainer interconnects all of the rolling elements and causes the rolling elements to circumferentially move in unison with one another. The retainer is rotatable about the axis with limited relative rotation with respect to the inner race, a first biasing element is supported in the retainer to radially bias the retainer position relative to the inner race such that each of the rollers is held at the midpoint of the plat cam surfaces in the inner race. An actuation disk is connected to the retainer by a means which allows some axial movement of the activation disk with respect to the retainer toward the case end. The preferred method would include a retainer tab extending axially from one end of the retainer and a notch which is adapted to engage the retainer tab thereby preventing circumferential or relative rotationally motion of the actuation disk relative to the retainer and allowing axial motion of the actuation disk relative to the retainer. A second biasing element is disposed between the actuation disk and the inner axial surface of the case end to bias the actuation disk away from the case end.
The clutch assembly includes an actuator to selectively overcome the second biasing element to force the actuation desk into contact with the case end, wherein rotation of the outer race and case end with respect to said inner race is frictionally transferred to the actuation disk and the retainer, overcoming the first biasing element, thereby moving the rolling elements along the cam surfaces to a position where the rolling elements engage and wedge between the inner and outer races to prevent relative rotation between the inner and outer races, thereby preventing rotation of the drop shaft of the transmission and movement of the vehicle.